rett syndrome
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Rett Syndrome. Presented by: Ashley Owen University of Wisconsin-Eau Claire November 30, 2004. What is RTT?. - PowerPoint PPT PresentationTRANSCRIPT
Rett Syndrome
Presented by: Ashley Owen
University of Wisconsin-Eau Claire
November 30, 2004
What is RTT?
Neurodevelopmental disorder cased by mutations in the methyl-CpG-binding protein 2 (MECP2) and is characterized by the loss of acquired skills after a period of normal development in infant girls.
Symptomsafter 7 to 18 months
Mild learning difficulties Disturbances with
breathing and cardiac rate
Bowel immobility Screaming fits Autistic features Microcephaly Seizures
Hand stereotypes Washing, clapping,
mouthing
Decrease in head growth
Small statue Teeth grinding “eye pointing”
Inheritance
Prevalence 1/10,000-15,000 females
X-linked dominant mutation De novo Inherited from parent with the disease causing
mutation and germline mosaicismMother would have XCI and be unaffected
Males
47, XXY Identified as RTT
Somatic mosaicism XCI
46, XY Severe neonatal encephalopathy
Leads to death“Disease of the brain”
Gene of Interest: MECP2
Methyl-CpG-Binding Protein Two domains
Methyl-CpG-binding domain (MBD) Transcriptional repression domain (TRD)
Location: Xq28 Pericentromeric heterochromatin
Transcriptional silencing/repression, epigenetic regulation, nuclear structure (chromatin) 5-methylcytosine rich heterochromatin
MBDNan, X., Meehan, R.R., & Bird, A.
Located between amino acid 89 and 162
Symmetrical methylated CpG dinucleotides
Binds to minor groove of beta DNA
MBD(cont.) Nan, X., Meehan, R.R., & Bird, A.
Dimerization is not required for binding Monomer
MBD and TRD are important for XCI Methyl dependent
repression
TRD
Interacts with co-repressor Sin3A Recruits histone deactylases
Exons
Exon 1 Non-coding 5‘
untranslated region (UTR)
Exon 2 Coding sequence
Exon 3 Coding sequence
Exon 4 Non-coding 3‘ UTR Coding sequence Polyadenylation creates
different protein lengths
Structure of Human MECP2Wan, M., et.al.
DetectionLewis, J.D., et.al.
Looking for MECPs expression clone
Methylated and unmethylated probe
Differ from MECP1 MECP1 is a 120kb Tissue distribution
Testis Anion/cation ion exchange
column Binding specificities
12 methyl-CpGs vs. a pair
Obtaining cDNALewis, J.D., et.al.
Partial amino acid sequence as a primer
340 bp fragment from original PCR to complete library λZAPll
ORF 492 amino acids and all 6 major peptides
Translational Experiments Lewis, J.D., et.al.
SDS-polyacrylamide Relationship between
ORF and MECP2 Showed an 81kd
sequence cDNA fused into E.Coli
with ß-galactosidase gene
Bound to methylated probe
Conclusion: ORF codes for MECP2
Localization Lewis, J.D., et.al.
Immunofluorescence Ab76 serum
Stained in heterochromatin areas
Parallel satellite DNA in mice Contains 8 CpGs sights
Associated with pericentromeric heterochromatin
Comparison of Mouse and Human MECP2
Reichwald, K., et.al.
•Identity between the mouse and human gene is 68% (average)
Mechanism
Expressed during organogenesis during embryonic life and in the hippocampus during adult life Other methylated binding proteins take over in
other cells during adulthood
Believed to be involved in XCI and genetic imprinting
Tissue Specific
Two transcripts 1.9kb ~10kb
Difference in tissue expression Difference in
translatability Half life is similar
Mutations
99.5% are sporadic Nonsense, missense/frameshifts, deletions
Majority are nonsense Detected using PCR and restriction enzyme
analysis Occur in CpG sites
HypermutableMethylated in germline and prone to deamination (C to T)
Mutations(Cont.)Wan, M., et.al.
See word document
Structure of Human MECP2Wan, M., et.al.
TreatmentNo trxt has shown significant improvements
Previous trxts L-carnitine
Fatty acid metabolism Respiratory features
Ketogenic diet Control of seizures Lacked vitamins
Naltrexone* Oral opiate antagonist Respiratory features,
EEG patterns
Ongoing trial Folate-Betaine
Methyl-donor group Alter gene expression Recruit other methyl
binding groups
Current trxt Supportive/symptomatic
therapy Occupational/physical
therapy
Social and Ethical Dilemmas
Money…testing in general is expensive Have to show clinical signs/family member Diagnostic testing
Test for mutation prenatallyPossible involvement with other disorders
Mental retardation in males
References
Hagberg, B.A. and Skjeldal, O.H. (1994). Rett variants: A suggested model for inclusion criteria. Pediatric Neurology, 11, 5-11.
Lewis, J.D., et.al. (1992). Purification, sequence, and cellular localization of a novel chromosomal protein that binds to methylated DNA. Cell, 69, 905-914.
Nan, X., Meehan, R.R., & Bird, A. (1993). Dissection of the methyl-CpG binding domain from the chromosomal protein MeCP2. Nucleic Acids Research, 21, 4886-4892.
Percy, A. K. (2002). Clinical trials and treatment prospects. Mental Retardation and Developmental Disabilities Research Reviews, 8, 106-111.
Reichwald, K., et.al. (2000). Comparative sequence analysis of the MECP2-locus in human and mouse reveals new transcribed regions. Mammalian Genome, 11, 182-190.
Rett Syndrome, RTT. (2004). Online mendelian inheritance in man, 9 Oct. 2004. Shahbazian, M.D., Antalffy, B., Armstrong, D.L. & Zoghbi, H.Y. (2002). Insight into rett
syndrome: MECP2 levels display tissue- and cell-specific difference and correlate with neuronal maturation. Human Molecular Genetics, 11, 115-124.
Wan, M. et.al. (1999). Rett syndrome and beyond: Recurrent spontaneous and familial MECP2 mutations at CpG hotspots. American Journal of Human Genetics, 65, 1520-1529.
Zoghbi, H.Y. (2004). Rett Syndrome. GeneReviews, www.genetests.org, 29 Sept. 2004.
Questions